A Ni-based heat-resistant superalloy, such as a 718 alloy, has been widely used as an aircraft engine or a gas turbine for power generation. Along with the gas turbine has been improved to have high performance and fuel efficiency, components resistant to higher temperature are required. In order to improve the heat resistance of the Ni-based heat-resistant super alloy, it is most effective to increase an amount of gamma prime (hereinafter referred to as γ′) phase that is a precipitation strengthening phase composed of an intermetallic compound represented by a composition such as Ni3(Al, Ti). It is required that the γ′ molar ratio in the Ni-based heat-resistant super alloy is much more increased to satisfy the high heat resistance and high strength.
However, increase of the γ′ phase makes it difficult to forge the alloy due high deformation resistance during hot working. Furthermore, as the γ′ molar ratio becomes greater, segregation tends to generate during casting solidification, and the ingot includes more high-temperature unstable phases and casting defects, as well as the ingot becomes less hot-forgeable. In addition, a large amount of Al and Ti, which are γ′ forming elements, makes the alloy have a lower solidus temperature and a higher recrystallization temperature of the alloy, and thus a temperature range in which the alloy can be forged becomes narrowed, since hot forging is in general conducted at a temperature not higher than the solidus temperature and not lower than the recrystallization temperature. Conventionally, it has been considered to be difficult to hot-forge an alloy including the γ′ phase by not less than 40% by mol, since there is practically no temperature range for forging. Accordingly, it has been proposed for producing the Ni-based heat-resistant super alloy having a high γ′ molar ratio to avoid the difficulty of forging working, such as cast products that is used as cast or a powder metallurgy process for producing an initial ingot by sintering (for example, see JP 10-46278 A (Patent Literature 1)).